Solid electrolytic capacitor and method of manufacturing a solid electrolytic capacitor

ABSTRACT

Provided is a method for forming a capacitor. The method includes:
     providing an anode with a dielectric thereon and a conductive node in electrical contact with the anode;   applying a conductive seed layer on the dielectric;   forming a conductive bridge between the conductive seed layer and the conductive node;   applying voltage to the anode;   electrochemically polymerizing a monomer thereby forming an electrically conducting polymer of monomer on the conductive seed layer;   plating a metal layer on said conductive polymer; and   disrupting the conductive bridge between the conductive seed layer and the conductive node.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part application of U.S. patentapplication Ser. No. 13/238,037 filed Sep. 21, 2011 which, in turn,claims priority to U.S. Provisional Patent Application No. 61/384,785filed Sep. 21, 2010 both of which are incorporated herein by reference.This application also claims priority to U.S. Provisional Patent Appl.No. 61/766,454 filed Feb. 19, 2013 which is incorporated herein byreference.

BACKGROUND

The present invention is related to a solid electrolytic capacitor and amethod of manufacturing a solid electrolytic capacitor. Morespecifically, the present invention is related to a method of forming aconductive bridge for improved formation of a cathode comprising anelectrochemically polymerized intrinsically conducting polymer and metallayer.

Solid electrolytic capacitors are well known in the art. Solidelectrolytic capacitors comprising an intrinsically conductive polymericcathode are also well known. A particular problem with solidelectrolytic capacitors comprising an intrinsically conducting polymericcathode is the cost of manufacturing, variation in polymer coverage andthe buildup, or thickness, within each part and from part to part.Manufacturing cost is associated with two things. One is the repetitivenumber of dip/dry cycles required for chemical in-situ polymerizationwhich is required to achieve sufficient coverage. The other is the costand complexity of the equipment with the current methods ofelectrochemical polymerization.

Due to the highly resistive nature of the dielectric it is difficult toform the polymeric coating by passing current through the dielectricfrom the anode. To avoid this problem a conductive seed layer istypically formed on the dielectric then an external electrical contactis placed in contact with the conductive seed layer. This arrangementtypically requires complex hardware or limits product design to thosethat allow for the external connection. The traditional externalconnection methods have a high potential for damage to the activesurface of the element. This damage occurs in current manufacturingmethods which require a direct physical contact between the externalhardware and the conductive seed layer. The external hardware isincompatible with the dielectric and physical damage to the dielectricand/or polymeric cathode layer is common. Damage to the polymericcathode layer may result in insufficient polymer coverage of thedielectric, that could lead to subsequent cathode layers damaging thedielectric properties, or subsequent processing damage of the exposeddielectric.

The present invention provides a very efficient method of forming aconductive polymeric coating whereby the external electrical contact isimproved by the process of electrically separating the externalelectrical contact from the active cathode region of the element. Thisis accomplished without detrimental impact on the polymer quality,either physically or electrically, or the underlying dielectric andanode layers.

SUMMARY

It is an object of the invention to provide an improved solidelectrolytic capacitor.

It is another object of the invention to provide a method of forming asolid electrolytic capacitor which is more efficient and which mitigatesthe problems of capacitor formation commonly realized in the art.

These and other advantages, as will be realized, are provided in amethod for forming a capacitor. The method includes:

providing an anode with a dielectric thereon and a conductive node inelectrical contact with the anode;

applying a conductive seed layer on the dielectric;

forming a conductive bridge between the conductive seed layer and theconductive node;

applying voltage to the anode;

electrochemically polymerizing a monomer thereby forming an electricallyconducting polymer of monomer on the conductive seed layer;

electroplating a metal layer in electrical contact with saidelectrically conducting polymer; and

disrupting the conductive bridge between the conductive seed layer andthe conductive node.

Another embodiment is provided in a method for forming a capacitorincluding:

providing an anode with a dielectric thereon and a conductive node inelectrical contact with the anode;

forming an insulator on the dielectric;

applying a conductive seed layer on the dielectric;

forming a conductive bridge between the conductive seed layer and theconductive node;

applying voltage to the anode;

electrochemically polymerizing a monomer thereby forming an electricallyconducting polymer of monomer on the conductive seed layer;

forming a metal layer, preferably by electroplating, in electricalcontact with said electrically conducting polymer; and

disrupting the electrical conductivity between the conductive seed layerand conductive node.

Yet another embodiment is provided in a method for forming a capacitorcomprising:

providing a process carrier;

providing an anode attached to the process carrier wherein the anodecomprises a dielectric thereon;

applying a conductive seed layer on the dielectric;

forming a conductive bridge between the conductive seed layer and theprocess carrier; applying voltage to the process carrier;

electrochemically polymerizing a monomer thereby forming an electricallyconducting polymer of the monomer on the conductive seed layer;

forming a metal layer, preferably by electroplating, in electricalcontact with said electrically conducting polymer; and

disrupting the conductive bridge between the conductive seed layer andthe process carrier.

Yet another advantage, as will be realized, is provided in a method forforming a capacitor. The method includes:

providing an anode comprising a dielectric thereon;

applying a conductive seed layer on the dielectric;

forming a conductive bridge between the conductive seed layer and anexternal electrical contact;

applying voltage to the external electrical contact;

electrochemically polymerizing a monomer thereby forming an electricallyconducting polymer of monomer on the conductive seed layer;

electrochemically forming a metal layer in electrical contact with saidelectrically conducting polymer; and

disrupting the connection of the conductive bridge between theconductive seed layer and the external electrical contact.

Yet another embodiment is provided in a method for forming a capacitor.The method includes:

providing an anode with a dielectric on the anode and a conductive nodein electrical contact with the anode;

forming a conductive path between the conductive node and an activecathode region wherein the active cathode region is on the dielectric;

applying voltage to the anode;

electrochemically polymerizing a monomer thereby forming an electricallyconducting polymer of the monomer in the active cathode region;

forming a metal plated layer on said electrically conducting polymer;and

disrupting the conductive path between the conductive node and theactive cathode region.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a top schematic view of an embodiment of the invention.

FIG. 2 is a cross-sectional schematic view of an embodiment of theinvention.

FIG. 3 is a cross-sectional schematic view of an embodiment of theinvention.

FIG. 4 is a cross-sectional schematic view of an embodiment of theinvention.

FIG. 5 is a cross-sectional schematic view of an embodiment of theinvention.

FIG. 6 is a cross-sectional schematic view of an embodiment of theinvention.

FIG. 7 is a cross-sectional schematic view of an embodiment of theinvention.

FIG. 8 is a cross-sectional schematic view of an embodiment of theinvention.

DESCRIPTION

The present invention is related to an improved solid electrolyticcapacitor and a method of manufacturing a solid electrolytic capacitor.More specifically, the present invention is related to a capacitor withan improved conductive polymeric cathode and plated metal layer and animproved method of forming the conductive polymeric cathode and platedmetal layer.

The invention will be described with reference to the figures which forman integral, non-limiting, component of the disclosure. Throughout thevarious figures similar elements will be numbered accordingly.

An embodiment of the invention will be described with reference to FIG.1 which is a schematic top view of a film, 10, with an anode and adielectric thereon. At least one conductive node, 12, and preferably aplurality of conductive nodes, is in electrical contact with the anodeand in one embodiment the conductive nodes extend outward through thedielectric from the anode. An insulator, 14, is illustrated the purposeof which will be further described herein.

An embodiment of the invention is illustrated in cross-sectionalschematic view in FIG. 2. In FIG. 2, a film comprising an anode, 16,with a dielectric, 18, thereon is represented collectively at 10. Theconductive node, 12, is in electrical contact with the anode, 16. Aconductive seed layer, 20, forms a conductive film preferably over theentire dielectric and insulator, 14, and the conductive seed layer is indirect electrical contact with the conductive node. As would berealized, voltage applied to the anode passes through the anode, theconductive node and throughout the conductive seed layer therebyproviding a charge over the surface of the dielectric. Current does notpass directly through the dielectric since the dielectric has higherresistance than the conductive node. The conductive polymer, 22, isformed by in-situ electrochemical polymerization of a monomer onto thesurface of the conductive seed layer. The conductive polymer, 22, isformed in at least the active cathode region, 21. A metal layer, 23, isformed on the conductive polymer layer preferably with voltage passingthrough the conductive node. After the conductive polymer and metallayer are formed the conductivity between the anode and the cathodelayer, comprising the conductive polymer and plated metal, is disruptedwithin the boundaries of the insulator, 14, such as along dotted line24, resulting in conductive layers separated by a dielectric therebyforming a capacitor. A carbon containing layer is preferably formedprior to the metal layer, as known in the art, to improve adhesion ofthe metal layer. For the purposes of discussion the anode is designatedas 16 throughout the specification with the cathode being the collectionof conductive layers opposite the dielectric from the anode. One ofskill in the art would realize that this is for convenience and theanode and cathode could be exchanged either physically or by reversemounting the capacitor, if valve metals are not used, thereby changingthe terminology, with regards to convention, without departing from thescope of the invention. In this embodiment the conductive seed layer isacting as both the conductive seed layer and a conductive bridge. Theembodiment of FIG. 2 after disruption, such as by laser ablation, isillustrated in cross-sectional schematic view in FIG. 3.

An embodiment of the invention is illustrated in cross-sectionalschematic view in FIG. 4. In FIG. 4, the anode, 16, with a dielectric,18, thereon are taken together at 10. The conductive node, 12, is inelectrical contact with the anode, 16. A conductive seed layer, 20,forms a conductive film preferably over the entire dielectric and atleast to the insulator, 14. The insulator may function as a dam with theconductive seed layer terminating at the insulator or, alternatively,the conductive seed layer may extend to, and even past, the conductivenode, 12, thereby covering the conductive node. A conductive bridge, 26,which is a coating, extends from and forms an electrical contact betweenthe conductive seed layer, 20, and the conductive node thereby forming aconductive path from the anode, through the conductive node and bridgeto the conductive seed layer. The conductive path through the conductivenode and conductive bridge has lower resistance than the conductive paththrough the dielectric. Voltage is applied thereby forming a conductivepolymer, 22, in at least the active cathode region, 21. Additionalvoltage is applied to form a plated metal layer, 23, over the conductivepolymer, 22. After formation of the conductive polymer and plated metallayer the conductivity of the bridge is disrupted within the bounds ofthe insulator, such as at 28, thereby electrically separating the anodefrom the conductive polymer and plated metal layer as illustrated inFIG. 5.

An embodiment of the invention is illustrated in cross-sectionalschematic view in FIG. 6. In FIG. 6 the anode, 16, with a dielectric,18, thereon are taken together as 10. An insulator, 14, prohibits theconductive seed layer, 20, from migrating up the dielectric therebyterminating the conductive seed layer at the insulator. A conductivenode, 12, forms an electrical contact between the anode and theconductive seed layer, 20, thereby establishing a favorable path ofelectrical conduction since the path through the dielectric has higherresistance. After formation of the conductive polymer layer, 22, andplated metal layer, 23, in at least the active cathode region, 21, theelectrical conductivity between the anode and the cathode is disrupted,such as at line 30, thereby forming a capacitor with electricallyisolated conductive layers with a dielectric there between asillustrated in FIG. 7.

An embodiment of the invention is illustrated in cross-sectionalschematic view in FIG. 8. In FIG. 8, the anode, 16, with a dielectric,18, thereon. A conductive seed layer, 20, is formed on the dielectricpreferably terminating at an insulator, 14. A conductive bridge, 26,provides an electrical connection between the conductive seed layer, 20,and at least one of a process carrier, 50, or an external electricalconnection, 52. Voltage is applied to either the process carrier or theexternal electrical connection and a conductive polymer layer, 22, isformed by in-situ electrochemical polymerization of a monomer, in atleast the active cathode region, 21, followed by electroplating at themetal layer, 23. After the conductive polymer layer and metal layer arecomplete the conductivity of the conductive bridge is disrupted,preferably at 54, thereby forming an electrolytic capacitor.

The electrical conductivity can be disrupted by any method suitable fordisrupting current flow through a conducting layer or element. Thedisruption can be done by, but not limited to, removal, destruction,oxidation, vaporization, abrasion, ablation, chemical treatment, thermaltreatment, etc. A particularly preferred method for disrupting thecurrent flow is laser ablation wherein conductive material is treatedwith a laser thereby removing, by ablation or vaporization, materialtreated thereby. Furthermore, the heat of ablation may locally oxidizethe conductive polymer, or the equivalent thereof, thereby renderingthat portion of the polymer which is oxidized non-conductive.

The conductive bridge is a coated material which forms a path ofelectrical conductivity with a resistance which is lower than theresistance of the dielectric, and preferably with a resistance of nomore than 10⁴Ω, with the path of electrical conductivity, typically butnot limited to, spanning between the conductive node and the conductiveseed layer. The conductive seed layer promotes electrochemicalpolymerization on the dielectric, over the conductive seed layer,without adverse reaction with the dielectric. The conductive bridge iscomposed of a material with properties common to existing cathodicmaterials, in that, the material is compatible with the dielectric, interms of low leakage current properties and protective aspects, andexhibits those same properties even while remaining in contact with thedielectric during product operation. Particularly preferred materialsfor use in the conductive bridge are manganese dioxide and conductingpolymer. While not limited thereto, a conductive polymer which is thesame as the conductive polymer being formed over the conductive seedlayer is preferred due to manufacturing simplicity and certainty ofcompatibility. The conductive polymer bridge can be formed by in-situpolymerization or by application of a polymer slurry followed by drying.

The conductive node is a region that forms a path with an electricalresistance which is lower than the electrical resistance through thedielectric. The conductive node can be a current path through thedielectric, a semi-conductor, or a conductor and most preferably theconductive node is conductive. The resistivity of the conductive node ispreferably no more than 10⁴Ω and even more preferably no more than 10²Ω.It is preferable that the conductive node comprises a material, or iscoated with a material, which prevents the formation of oxides in thepresence of moisture during current flowing through the conductive node.Noble metals, stainless steel and carbon are mentioned as particularlysuitable for demonstration of the invention.

The insulator material is preferably a polymer selected from an epoxy, apolyimide, a polyamide, a siloxane, and a silicone. The insulatorprovides two functions. One function of the insulator is to act as a damwhereby wicking of monomer, or any solution, is prohibited beyond theinsulator. Another function is to provide a buffer between thedisruption of electrical conductivity and the dielectric. For example,when the electrical disruption occurs over the insulator a portion ofthe insulator can remain without detriment thereby mitigating anypotential detrimental effects of laser impingement on the dielectric.

For the purposes of the present invention a direct electrical contact isdefined as an electrical contact between two components in physicalcontact. An indirect electrical contact is defined as an electricalcontact between two components with a conductor, such as conductiveadhesive, there between.

The conductive seed layer is preferably a thin layer of a conductivematerial such as manganese dioxide or a conductive polymer. Theconductive seed layer may be a seed layer which spreads the charge overa portion of the dielectric thereby improving the formation of in-situelectrochemically formed conductive polymer. Manganese dioxide can beused in the form of islands wherein the islands are electricallyconnected by conductive polymer as the conductive polymer grows.Alternatively, the manganese dioxide can cover the entire underlyingsurface. A thin layer of conductive polymer, and most preferably thesame conductive polymer as that being formed on the conductive seedlayer, can be used. The thin layer of conductive polymer for theconductive seed layer can be formed by dip coating with polymer slurryor by in-situ polymerization.

The plated metal layer is provided to enhance subsequent connectivity toexternal termination, such as a lead frame. A carbon containing layermay be included if desired. The metal preferably a metal which issolderable such as a layer containing silver, nickel, copper or goldwith silver or nickel being most preferred.

The anode preferably includes a valve metal or a conductive oxide of avalve metal with aluminum, tantalum, niobium, titanium, hafnium,zirconium, zinc, tungsten, bismuth, antimony and niobium oxide beingmentioned as particularly suitable for demonstration of the instantinvention. Niobium, tantalum, aluminum, and NbO are particularlypreferred as the anode.

The dielectric is preferably an oxide of the anode without limitthereto. The formation of dielectrics on an anode, and particularly avalve metal anode, is widely documented and well understood in the artand further elaboration herein is not warranted. The active cathoderegion is the region of the capacitive element that is to be coated bythe in-situ electrochemically polymerized polymer. In the includedembodiments this is typically covered by the conductive seed layer topromote even growth of the in-situ electrochemically polymerizedpolymer, though is not defined by the conductive seed layer, as theconductive seed layer may extend beyond, or have less coverage, thanthat of the active cathode region. The active cathode region is alsopreferred to be in contact with the surface of the anode dielectric.

The cathode layer is a conductive layer preferably comprising conductivepolymer, such as polythiophene, polyaniline, polypyrrole or theirderivatives, manganese dioxide, lead oxide or combinations thereof. Anintrinsically conducting polymer is most preferred.

A particularly preferred conducting polymer is illustrated in Formula I:

R¹ and R² of Formula 1 are chosen to prohibit polymerization at theβ-site of the ring. It is most preferred that only α-site polymerizationbe allowed to proceed. Therefore, it is preferred that R¹ and R² are nothydrogen. More preferably, R¹ and R² are α-directors. Therefore, etherlinkages are preferable over alkyl linkages. It is most preferred thatthe groups are small to avoid steric interferences. For these reasons R¹and R² taken together as —O—(CH₂)₂—O— is most preferred. In Formula 1, Xis S or N and most preferable X is S.

R¹ and R² independently represent linear or branched C₁-C₁₆ alkyl orC₂-C₁₈ alkoxyalkyl; or are C₃-C₈ cycloalkyl, phenyl or benzyl which areunsubstituted or substituted by C₁-C₆ alkyl, C₁-C₆ alkoxy, halogen orOR³; or R¹ and R², taken together, are linear C₁-C₆ alkylene which isunsubstituted or substituted by C₁-C₆ alkyl, C₁-C₆ alkoxy, halogen,C₃-C₈ cycloalkyl, phenyl, benzyl, C₁-C₄ alkylphenyl, C₁-C₄ alkoxyphenyl,halophenyl, C₁-C₄ alkylbenzyl, C₁-C₄ alkoxybenzyl or halobenzyl, 5-, 6-,or 7-membered heterocyclic structure containing two oxygen elements. R³preferably represents hydrogen, linear or branched C₁-C₁₆ alkyl orC₂-C₁₈ alkoxyalkyl; or are C₃-C₈ cycloalkyl, phenyl or benzyl which areunsubstituted or substituted by C₁-C₆ alkyl.

The conducting polymer is preferably chosen from polypyrroles,polyanilines, polythiophenes and polymers comprising repeating units ofFormula I, particularly in combination with organic sulfonates: Aparticularly preferred polymer is 3,4-polyethylene dioxythiophene(PEDT).

The manganese dioxide layer is preferably obtained by immersing an anodeelement in an aqueous manganese nitrate solution. The manganese oxide isthen formed by thermally decomposing the nitrate at a temperature offrom 200 to 350° C. in a dry or steam atmosphere. The anode may betreated multiple times to insure optimum coverage.

As typically employed in the art, various dopants can be incorporatedinto the polymer during the polymerization process. Dopants can bederived from various acids or salts, including aromatic sulfonic acids,aromatic polysulfonic acids, organic sulfonic acids with hydroxy group,organic sulfonic acids with carboxylhydroxyl group, alicyclic sulfonicacids and benzoquinone sulfonic acids, benzene disulfonic acid,sulfosalicylic acid, sulfoisophthalic acid, camphorsulfonic acid,benzoquinone sulfonic acid, dodecylbenzenesulfonic acid, toluenesulfonicacid. Other suitable dopants include sulfoquinone,anthracenemonosulfonic acid, substituted naphthalenemonosulfonic acid,substituted benzenesulfonic acid or heterocyclic sulfonic acids asexemplified in U.S. Pat. No. 6,381,121 which is included herein byreference thereto.

Binders and cross-linkers can be also incorporated into the conductivepolymer layer if desired. Suitable materials include poly(vinylacetate), polycarbonate, poly(vinyl butyrate), polyacrylates,polymethacrylates, polystyrene, polyacrylonitrile, poly(vinyl chloride),polybutadiene, polyisoprene, polyethers, polyesters, silicones, andpyrrole/acrylate, vinylacetate/acrylate and ethylene/vinyl acetatecopolymers.

It is preferred to include a dopant in the polymer. The dopant can becoated separately or included in the monomer solution. A particularlypreferred dopant is the sodium salt of polystyrenesulfonate (PSS).

The present invention has been described with particular reference tostated embodiments without limit thereto. One of skill in the art wouldrealize additional embodiments, alternatives and improvements which arenot specifically stated but which are within the metes and bounds of theclaims appended hereto.

The invention claimed is:
 1. A method for forming a capacitorcomprising: providing an anode; forming a dielectric on said anode;forming a conductive bridge between an external electrical connectionand an active cathode region wherein said active cathode region is onsaid dielectric; applying voltage to said external electricalconnection; electrochemically forming at least one cathode layer on saidactive cathode region; and disrupting said conductive bridge betweensaid external electrical connection and said active cathode region. 2.The method for forming a capacitor of claim 1 wherein said at least onecathode layer is a manganese dioxide layer.
 3. The method for forming acapacitor of claim 1 wherein said at least one cathode layer is anintrinsically conducting polymer.
 4. The method for forming a capacitorof claim 1 wherein said at least one cathode layer is a metal layer. 5.The method for forming a capacitor of claim 4 further comprising forminga carbon containing layer prior to forming said metal layer.
 6. Themethod for forming a capacitor of claim 4 further comprising forming acarbon containing layer prior to forming said metal layer.
 7. The methodfor forming a capacitor of claim 1 wherein said electrochemicallyforming at least one cathode layer comprises elecrolytically forming ametal layer on said cathode region.
 8. The method for forming acapacitor of claim 7 wherein said elecrolytically forming of said metallayer comprises electroplating of metal through said conductive bridge.9. The method for forming a capacitor of claim 8 wherein said metallayer comprises a metal selected from the group consisting of silver,nickel, copper and gold.
 10. The method for forming a capacitor of claim9 wherein said metal layer comprises a metal selected from the groupconsisting of silver and nickel.
 11. The method for forming a capacitorof claim 1 wherein said electrochemically forming at least one cathodelayer comprises elecrolytically forming a manganese dioxide layer onsaid cathode region.
 12. The method for forming a capacitor of claim 1wherein said active cathode region is at least partially covered by aconductive seed layer.
 13. The method for forming a capacitor of claim12 wherein said conductive seed layer comprises a material selected frommanganese dioxide and a conductive polymer.
 14. The method for forming acapacitor of claim 1 wherein said conductive bridge comprises aconductive seed layer.
 15. The method for forming a capacitor of claim 1further comprising: forming an insulator on said dielectric.
 16. Themethod for forming a capacitor of claim 15 wherein said conductivebridge extends over said insulator.
 17. The method for forming acapacitor of claim 1 wherein said conductive bridge is electricallyconnected to a process carrier.
 18. The method for forming a capacitorof claim 1 wherein said disrupting said conductive bridge compriseslaser ablation.
 19. The method for forming a capacitor of claim 1wherein said conductive bridge comprises a material selected frommanganese dioxide and conductive polymer.
 20. The method for forming acapacitor of claim 1 wherein said disrupting said electricalconductivity comprises disrupting conductivity of said conductivebridge.
 21. The method for forming a capacitor of claim 1 wherein saidanode is selected from the group consisting of a valve metal and aconductive oxide of a valve metal.
 22. The method for forming acapacitor of claim 21 wherein said anode is selected from the groupconsisting of aluminum, tantalum, niobium and NbO.